The Role of Dithiocarbamate Catalysts in the Diversification of Sulfur Speciation Towards Anionic Sulfur.

Recently, there has been growing interest in the implementation of various "catalysts" to further diversify the substrate scope for inverse vulcanization reactions. While there have been several proposals on the mechanism of how these catalysts work, the speciation of sulfur in these mixtures has remained elusive. As a key component to understanding when and if these catalysts are appropriate, we sought to elucidate the role of dithiocarbamate species in inverse vulcanization reactions by attempting to characterize the speciation of sulfur. The reaction efficacy for various substrates containing different functional groups with sulfur, either with or without a metal dithiocarbamate, potassium diethyldithiocarbamate (K-DTC), suggests the formation of a rapidly fluctuating sulfur speciation and, most importantly, the presence of anionic sulfur. The work concludes with some suggestions on best practices for the utilization of dithiocarbamate catalysts based on our results.

Influencing the Crystalline Domains of Poly(vinylidenedifluoride) Composites Using Fluorinated Silica Nanoparticles as Drop-In Modifiers.

Improvements to fluoropolymer processing techniques by way of utilizing nanoparticles as drop-in processing aids have pronounced effects on bulk composite properties. In this work, we prepared fluoroalkyl-silanized silica nanoparticles (F-SiNPs, ca. 200 nm) that were solvent-blended with polyvinylenedifluoride (PVDF) in order to prepare composites with varying weight fractions. We demonstrated that the ability to functionalize SiNPs with long fluoroalkylchains that induced co-crystallization with the PVDF matrix, resulting in uniform particle dispersion and improved interlaminate adhesion. This was quantitatively investigated using calorimetry and thermogravimetric analysis, which showed a decrease in the bulk crystallinity of the virgin PVDF from 37% to 10% with minimal 10 wt % F-SiNP loading, rendering a nearly amorphous PVDF. Additional discussions in this work include the effects of various bare and fluoroalkyl-functionalized SiNP loadings on the amorphous and crystalline domains of the PVDF matrix, as well as thermal decomposition.

Perfluoropyridine: Discovery, Chemistry, and Applications in Polymers and Material Science.

Perfluoropyridine (PFPy) is an organofluorine compound that has been employed for a variety of applications, from straightforward chemical synthesis to more advanced functions, such as fluorinated networks and polymers. This can be directly attributed to the highly reactive nature of PFPy, especially towards nucleophilic aromatic substitution (SNAr). The aim of this review is to highlight the discovery and synthesis of PFPy, discuss its reactive nature towards SNAr, and to summarize known reports of the utilization and thermal analysis of PFPy containing fluoropolymers and fluorinated network materials.

Fluoromaticity: The Molecular Orbital Contributions of Fluorine Substituents to the π-Systems of Aromatic Rings.

The addition of fluorine atoms to an aromatic ring brings about an additional set of π-bonding and antibonding orbitals culminating after the addition of the sixth fluorine with a new set of π-aromatic-like orbitals that affect the molecule in a way that we will refer to hereafter as "fluoromaticity". Depending on the number and position of the fluorine atoms, the contributed π-orbitals can even further stabilize the ring leading to smaller bond lengths within the ring and higher resistance to addition reactions. This added ring stability partially explains the high thermostability and chemical resistance found in polymers containing fluorinated aromatics in their architecture. A similar molecular orbital effect is seen with the addition of other halogen atoms to aromatic rings, though to a much smaller degree and not resulting in the additional ring stability.

Theoretical Prediction and Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyrimidine, Perfluoropyridazine, and Perfluoropyrazine.

Perfluoroaromatics, such as perfluoropyridine and perfluorobenzene, are privileged synthetic scaffolds in organofluorine methodology, undergoing a series of regioselective substitution reactions with a variety of nucleophiles. This unique chemical behavior allows for the synthesis of many perfluoroaromatic derived molecules with unique and diverse architectures. Recently, it has been demonstrated that perfluoropyridine and perfluorobenzene can be utilized as precursors for a variety of materials, ranging from high performance polyaryl ethers to promising drug scaffolds. In this work, using density functional theory, we investigate the possibility of perfluoropyrimidine, perfluoropyridazine, and perfluoropyrazine participating in similar substitution reactions. We have found that the first nucleophilic addition of a phenoxide group substitution on perfluoropyrimidine and on perfluoropyridazine would happen at a site para to one of the nitrogen atoms. While previous literature points to mesomeric effects as the primary cause of this phenomenon, our work demonstrates that this effect is enhanced by the fact that the transition states for these reactions result in bond angles that allow the phenoxide to π-complex with the electron-deficient diazine ring. The second substitution on perfluoropyrimidine and on perfluoropyridazine is most likely to happen at the site para to the other nitrogen. The second substitution on perfluoropyrazine is most likely to happen at the site para to the first substitution. The activation energies for these reactions are in line with those reported for perfluoropyridine and suggest that these platforms may also be worth investigation in the lab as possible monomers for high performance polymers.

Crystal Engineering Using Polyiodide Halogen and Chalcogen Bonding to Isolate the Phenothiazinium Radical Cation and Its Rare Dimer, 10-(3-Phenothiazinylidene)phenothiazinium.

Utilizing facile one-electron oxidation of 10H-phenothiazine by molecular diiodine, the solid-state structure of the 10H-phenothiazinium radical cation was obtained in three cation:iodide ratios, as well as its THF and acetone solvates. Oxidation of 10H-phenothiazine with molecular diiodine in DMSO or DMF provided the structure of the radical coupling product 10-(3-phenothiazinyldene)phenothiazinium, which has not been crystallographically characterized to date. The radical cations were balanced by a mixture (I7 )- , (I5 )- , (I3 )- , and I- anions, where a variety of chalcogen, halogen, and hydrogen bonding interactions stabilize the structures to reveal these interesting cationic species.

Halogen and Chalcogen Bonding Between the Triphenylphosphine Chalcogenides (Ph3 P=E; E=O, S, Se) and Iodofluorobenzenes.

A series of cocrystals of Ph3 P=E (E=O, S, Se) with organoiodines were studied to understand the roles of noncovalent interactions including chalcogen (ChB) and halogen (XB) bonding in their formation. The structure of the cocrystal of Ph3 P=S and 1,2-diiodotetrafluorobezene was determined, which demonstrates a similar chalcogen⋅⋅⋅iodine XB pattern to the previously reported isomorphic Ph3 P=Se structure. The cocrystalline structures resulting from the combination of 1,3-diiodotetrafluorobenzene (1,3-F4 DIB), as well as iodopentafluorobenzene, with all three triphenylphosphine chalcogenides, were also determined. The (Ph3 P=Se) ⋅ (1,3-F4 DIB) cocrystal presents a rare example of a selenium⋅⋅⋅organoiodine ChB. The observed ChB and XB interactions have normalized distance parameters (RXB ) ranging from 0.80 to 0.98. The strength of the XB and ChB interactions were analyzed using natural bond orbital (NBO) theory, with calculated energies falling between 3.14 kcal/mol and 12.81 kcal/mol.

Density Functional Theory Investigation of Fulvene-Derivatized Fullerenes as Candidates for Organic Solar Cells.

Interest within the scientific community in organic solar cells has been on the rise over the last two decades as researchers respond to increasing demands for alternative renewable energy sources. Fulvene, fullerene, and endohedral metallofullerene derivatives have individually shown great promise as efficient charge transfer agents. Despite the heavy demand for research in this area, there have been no studies reported to date that explore the electronic behavior of molecules containing both fullerene and fulvene groups. The lack of interest may be attributed to inherent limitations and inaccuracy in most density functional theory (DFT) band gap calculations for large molecules. Herein we present a systematic computational investigation of the band gaps and dipole moments of several test fullerene-fulvene molecules using a novel DFT method that has been modified to allow accurate computation of the band gaps of this class of molecules. Calculated results showed promising low band gap energies and attractive conductive properties for all fullerene-fulvene derivatives. This new DFT method can conceivably be an invaluable tool that can provide predictive insight into the suitability of similar high molecular weight materials for application in organic solar cell devices.

Correlation of Structure with Crystalline to Amorphous Phase Transitions of 1,3,6-Substituted Fulvene-Derived Molecular Glasses.

An investigation into the crystalline to amorphous phase transitions of prepared 1,3,6-substituted pentafulvenes showed the expected reversible heated melt and cooling recrystallization in only a few examples. Systematic incorporation of bulky substituents at the 6-position of the fulvene ring led to the nonreversible thermal behavior, rendering phases that were locked into glassy, vitrified states. These molecular glasses produced physically translucent and amorphous features with glass transition temperatures in the range of 61-77 °C, comparable with high-strength plastics such as polyethylene terephthalate. Additionally, the melting point transitions and the resulting heat of fusion values were found to be directly influenced by the nature of the 6-position substituent. Single crystal X-ray crystallography showed that in some cases, fulvenes possessing fused aromatics exhibited a high degree of intermolecular π-π stacking. These results point to a class of molecular glass formers as host materials possessing tunable bulk properties for potentially new optical applications.

Crystal structures of 6-cyclo-propyl-1,3-diphenylfulvene and 6-(2,3-di-meth-oxy-naphth-yl)-1,3-di-phenylfulvene.

The title compounds, 6-cyclo-propyl-1,3-diphenylfulvene, C21H18, [systematic name: 5-(cyclo-propyl-methyl-idene)-1,3-di-phen-yl-cyclo-penta-1,3-diene], 1, and 6-(2,3-di-meth-oxy-naphth-yl)-1,3-diphenylfulvene, C30H24O2, {systematic name: 5-[(3,4-di-meth-oxy-naphthalen-2-yl)methyl-idene]-1,3-di-phenyl-cyclo-penta-1,3-di-ene}, 2, were prepared from 1,3-di-phenyl-cyclo-penta-diene, pyrrolidine, and the corresponding aldehydes in an ethano-lic solution. Each structure crystallizes with one mol-ecule per asymmetric unit and exhibits the alternating short and long bond lengths typical of fulvenes. A network of C-H⋯C ring inter-actions as well as C-H⋯O inter-actions is observed, resulting in the compact packing found in each structure.

Single-crystal X-ray diffraction dataset for 3,5-difluoro-2,6-bis(4-iodophenoxy)-4-phenoxypyridine.

The data in this article are related to the research article "Utilizing the Regioselectivity of Perfluoropyridine towards the Preparation of Phenyoxyacetylene Precursors for Partially Fluorinated Polymers of Diverse Architecture."1 The X-ray structure analysis of 3,5-difluoro-2,6-bis(4-iodophenoxy)-4-phenoxypyridine has revealed an asymmetric unit containing two molecules, linked via both Type I and Type II C-I∙∙∙I-C halogen bonding interactions. The packing is further consolidated via Ar-H∙∙∙π interactions. This compound has been utilized for the synthesis of monomers for linear and network polymers.

Exploiting the Site Selectivity of Perfluoropyridine for Facile Access to Densified Polyarylene Networks for Carbon-Rich Materials.

Fluorinated molecules containing reactive functionalities are of great interest to the materials community as these compounds can be used to prepare fluorinated polymers with desirable physical and electronic properties. Despite their potential, many of these compounds are limited by their synthesis which generally requires transition-metal-catalyzed coupling reactions or harsh fluorinating conditions. Perfluoroheteroaromatic compounds provide a unique solution to this problem as compounds such as perfluoropyridine can undergo SNAr reactions with a wide range of simple nucleophiles in a controlled and regioselective manner. Herein we report the transition-metal-free synthesis of a pool of highly soluble high aromatic content (HAC) perfluoropyridine-based thermosetting precursors and compounds of interest which can be easily obtained from readily available chemical precursors using simple nucleophilic chemistries. These thermally active monomers cure readily, in 350-400 °C temperature ranges, into highly densified polyaryelene networks and demonstrate decomposition temperatures well above 400 °C and high char yields at 900 °C, making these promising materials for high-temperature applications as well as templates for carbon-based nanomaterials.

Theoretical Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyridine.

Pentafluoropyridine, a potentially useful precursor in organofluorine methodology, undergoes selective substitution of a fluorine with a phenoxide at the site para to the nitrogen. Subsequent aryloxide substitutions can be accomplished at the ortho-positions with aryloxide groups containing various functional groups para to the phenoxide oxygen. During this phase of the reaction, "reverse reactions" involving substitutions of the original para substituent with a free fluoride or with another aryloxide moiety are observed with a frequency that depends on the functional group para to the oxygen on the aryloxide. Herein, we provide a theoretical explanation of these observations through use of density functional theory.

Crystal structures of a series of 6-aryl-1,3-diphenyl-fulvenes.

The synthesis and crystal structures of a series of 6-aryl-fuvlenes (fulvene is 5-methyl-idene-cyclo-penta-1,3-diene) with varying methyl-ation patterns on the 6-phenyl substituent are reported, namely 6-(3-methyl-phen-yl)-1,3-di-phenyl-fulvene (C25H20), 6-(4-methyl-phen-yl)-1,3-di-phenyl-fulvene (C25H20), 6-mesityl-3-di-phenyl-fulvene (C27H24) and 6-(2,3,4,5,6-penta-methyl-phen-yl)-1,3-di-phenyl-fulvene (C29H28). The bond lengths are typical of those observed in related fulvenes. A network of C-H⋯π ring inter-actions consolidates the packing in each structure.

Crystal structures and Hirshfeld surface analysis of a series of 4-O-aryl-perfluoro-pyridines.

Five new crystal structures of perfluoro-pyridine substituted in the 4-position with phen-oxy, 4-bromo-phen-oxy, naphthalen-2-yl-oxy, 6-bromo-naphthalen-2-yl-oxy, and 4,4'-biphen-oxy are reported, viz. 2,3,5,6-tetra-fluoro-4-phen-oxy-pyridine, C11H5F4NO (I), 4-(4-bromo-phen-oxy)-2,3,5,6-tetra-fluoro-pyridine, C11H4BrF4NO (II), 2,3,5,6-tetra-fluoro-4-[(naphthalen-2-yl)-oxy]pyridine, C15H7F4NO (III), 4-[(6-bromo-naphthalen-2-yl)-oxy]-2,3,5,6-tetra-fluoropyridine, C15H6BrF4NO (IV), and 2,2'-bis-[(perfluoro-pyridin-4-yl)-oxy]-1,1'-biphenyl, C22H8F8N2O2 (V). The dihedral angles between the aromatic ring systems in I-IV are 78.74 (8), 56.35 (8), 74.30 (7), and 64.34 (19)°, respectively. The complete mol-ecule of V is generated by a crystallographic twofold axis: the dihedral angle between the pyridine ring and adjacent phenyl ring is 80.89 (5)° and the equivalent angle between the biphenyl rings is 27.30 (5)°. In each crystal, the packing is driven by C-H⋯F inter-actions, along with a variety of C-F⋯π, C-H⋯π, C-Br⋯N, C-H⋯N, and C-Br⋯π contacts. Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing.

Syntheses, crystal structures and Hirshfeld surface analyses of (3aR,4S,7R,7aS)-2-(perfluoro-pyridin-4-yl)-3a,4,7,7a-tetra-hydro-4,7-methano-iso-indole-1,3-dione and (3aR,4S,7R,7aS)-2-[(perfluoro-pyridin-4-yl)-oxy]-3a,4,7,7a-tetra-hydro-4,7-methano-iso-indole-1,3-dione.

The syntheses and crystal structures of the title compounds, C14H8F4N2O2 and C14H8F4N2O3, are reported. In each crystal, the packing is driven by C-H⋯F inter-tactions, along with a variety of C-H⋯O, C-O⋯π, and C-F⋯π contacts. Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing: they showed that the largest contributions to the surface contacts arise from H⋯F/F⋯H inter-actions, followed by H⋯H and O⋯H/H⋯O.

Electrowetting Behavior and Digital Microfluidic Applications of Fluorescent, Polymer-Encapsulated Quantum Dot Nanofluids.

Digital microfluidics is a liquid-handling technology capable of rapidly and autonomously controlling multiple discrete droplets across an array of electrodes and has seen continual growth in the fields of chemistry, biology, and optics. This technology is enabled by rapidly switching the wettability of a surface through the application of an electric field: a phenomenon known as electrowetting-on-dielectric. The results reported here elucidate the wetting behavior of fluorescent quantum dot nanofluids by varying the aqueous-solubilizing polymers, changing the size of the nanocrystals, and the addition of surfactants. Nanofluid droplets were demonstrated to have very large changes in contact angle (>100°) by employing alternating current voltage to aqueous droplets within a dodecane medium. The stability of quantum dot nanofluids is also evaluated within a digital microfluidics platform, and the optical properties are not perturbed even under high voltages (250 V). Multiple fluorescent droplets with varying emission can be simultaneously actuated and rapidly mixed (<10 s) to generate a new nanofluid with optical properties different from the parent solutions.

Recent Studies on Fluorinated Silica Nanometer-Sized Particles.

Since initially being reported, fluorinated silica nanometer-sized particles (F-SiNPs) have gained much interest in the scientific community, due to their unique properties. These properties, include, low surface energies, increased mechanical strength, thermal robustness, and chemical resistance, and are a direct result of the incorporation of fluorine with a nanometer-sized silica network. This review aims to summarize the synthetic methods that have, and are still, being utilized to prepare these specialized materials. Following this, applications for F-SiNPs, with an emphasis on recent examples, will be presented in further detail.

Coordination complexes of chromium(0) with a series of 1,3-diphenyl-6-aryl-fulvenes.

The synthesis and structural properties of a series of chromium tricarbonyl 'piano-stool' complexes bearing substituted penta-fulvene ligands were studied. The complexes, tricarbon-yl(1,3,6-tri-phenyl-fulvene)chromium(0) benz-ene hemisolvate, [Cr(C24H18)(CO)3]·0.5C6H6 (I), tricarbon-yl[1,3-di-phen-yl-6-(3-vinyl-phen-yl)fulvene]chromium(0), [Cr(C26H20)(CO)3] (II), and tricarbon-yl[1,3-diphenyl-6-(pyren-1-yl)fulvene]chromium(0), [Cr(C34H22)(CO)3] (III), each have a distorted octa-hedral geometry, with the fulvene coordinated in a π-η2:π-η2:π-η2 fashion. Significant deviation of the exocyclic fulvene double bond from the cyclo-penta-diene plane accompanies coordination. Evidence of non-covalent π-π inter-actions was observed in both (I) and (III), with centroid-to-centroid distances ranging from 3.330 (8) to 3.494 (8) Å.

Synthesis of reactive 1,3-diphenyl-6-aryl-substituted fulvene chromophores.

This data article describes a detailed synthetic strategy and experimental data for the synthesis of brominated fulvene chromophores as reactive precursors/monomers for conjugated organic materials. Metal-mediated coupling reactions of brominated fulvenes would result in conjugated small molecules or polymers that would find application as organic light emitting diodes (OLEDs) and photovoltaic (PV) applications.